joeblue83

Looking up upgrade after Dyno Don's y pipe. Would it make much sense to increase from my 3 inch catback to a 3.5 or even a 4 inch. Will the 2.5 inch y pipe even flow enough to fully use a 3.5 or 4 inch mufflex or should I keep my 3 inch on right now?

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383 Forged Stroker. Splayed 2 bolt mains, TPIS Miniram, ZZ409, Probuilt 700r4, Dart 200cc 2.05/1.60 Alum Heads, 3500 Stall, 12 bolt 3.91, Dyno Dons Headers and Y, All new Spohn rear suspension and crossmember torque arm. relocated battery,Working on 3.5 CAI and Mufflex
12.03 in the 1/4 with a 1.59 60 foot WITH TRANNY PROBS
Hoping for mid 11's next year

1989GTATransAm

Some things to ponder. Two 2.5" pipes equal 9.8 square inches. One 3.5" pipe equals 9.6 square inches. Pretty close. One 3" pipe equals 7 square inches.

joeblue83

So you really would not gain much going to a 4 over a 3.5 with a 2.5 inch y

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383 Forged Stroker. Splayed 2 bolt mains, TPIS Miniram, ZZ409, Probuilt 700r4, Dart 200cc 2.05/1.60 Alum Heads, 3500 Stall, 12 bolt 3.91, Dyno Dons Headers and Y, All new Spohn rear suspension and crossmember torque arm. relocated battery,Working on 3.5 CAI and Mufflex
12.03 in the 1/4 with a 1.59 60 foot WITH TRANNY PROBS
Hoping for mid 11's next year

Dyno Don

The other point to ponder....
You might need 9.8 sq. ins. at the collector,(when ex. is hot) but by the time the exhaust condenses down the line, you probably won't need more than 7.5 sq. ins.(because it cools and therefor reduces in volume).

In other words, there are plenty of 11 sec. & low 12 sec. cars using 3"

joeblue83

And having a 3 inch cutout right after the y pipe probably helps a bit also